From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49381C433EF for ; Fri, 15 Oct 2021 02:53:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 219BF611CC for ; Fri, 15 Oct 2021 02:53:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232508AbhJOCzn (ORCPT ); Thu, 14 Oct 2021 22:55:43 -0400 Received: from linux.microsoft.com ([13.77.154.182]:57546 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232233AbhJOCzm (ORCPT ); Thu, 14 Oct 2021 22:55:42 -0400 Received: from [192.168.254.32] (unknown [47.187.212.181]) by linux.microsoft.com (Postfix) with ESMTPSA id 4694820B9D1C; Thu, 14 Oct 2021 19:53:36 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 4694820B9D1C DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1634266417; bh=reCWsG+8xJilvrJz+WoV/MqKaWNhqFOL0FqgTlAI2sg=; h=Subject:To:References:From:Date:In-Reply-To:From; b=EanEkOCQy5YG4eDEX4v7Ne85rMLxanRPUkRO553AHaC85BMgw9XPvv54pr0INixiS g7TbE1VvrKLG5+GL6pAGx+Svaw5MOivvg2YXSf0TtpntbidFnhb/q8BTHZ1ki5Zs1B OwadxgDFVyjo/NVZVlLazzYHrYhh8Vgwk7H6qtok= Subject: Re: [PATCH v9 00/11] arm64: Reorganize the unwinder and implement stack trace reliability checks To: mark.rutland@arm.com, broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <20211015023413.16614-1-madvenka@linux.microsoft.com> From: "Madhavan T. Venkataraman" Message-ID: <4b3d5552-590c-e6a0-866b-9bc51da7bebf@linux.microsoft.com> Date: Thu, 14 Oct 2021 21:53:35 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20211015023413.16614-1-madvenka@linux.microsoft.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org My mailer screwed up the threading again. I am having Thunderbird woes. I will correct and resend as version 10. Please delete version 9 of this patch series. I profusely apologize for this annoyance. Madhavan On 10/14/21 9:34 PM, madvenka@linux.microsoft.com wrote: > From: "Madhavan T. Venkataraman" > > Make all stack walking functions use arch_stack_walk() > ====================================================== > > Currently, there are multiple functions in ARM64 code that walk the > stack using start_backtrace() and unwind_frame() or start_backtrace() > and walk_stackframe(). Convert all of them to use arch_stack_walk(). > This makes maintenance easier. > > This means that arch_stack_walk() needs to be always defined. So, > select CONFIG_STACKTRACE in the ARM64 Kconfig file. > > Consolidate the unwinder > ======================== > > Currently, start_backtrace() and walk_stackframe() are called separately. > There is no need to do that. Move the call to start_backtrace() into > walk_stackframe() so that walk_stackframe() is the only unwinder function > a consumer needs to call. > > The consumers of walk_stackframe() are arch_stack_walk() and > arch_stack_walk_reliable(). > > Rename unwinder functions > ========================= > > Rename unwinder functions to unwind*() similar to other architectures > for naming consistency. > > start_backtrace() ==> unwind_start() > unwind_frame() ==> unwind_next() > walk_stackframe() ==> unwind() > > Annotate unwinder functions > =========================== > > Annotate all of the unwind_*() functions with notrace so they cannot be > ftraced and NOKPROBE_SYMBOL() so they cannot be kprobed. Ftrace and Kprobe > code can call the unwinder. > > Redefine the unwinder loop > ========================== > > Redefine the unwinder loop and make it similar to other architectures. > Define the following: > > unwind_start(&frame, fp, pc); > while (unwind_continue(task, &frame, consume_entry, cookie)) > unwind_next(task, &frame); > > unwind_continue() > This new function implements checks to determine whether the > unwind should continue or terminate. > > unwind_next() > Same as the original unwind_frame() except: > > - the stack trace termination check has been moved from here to > unwind_continue(). So, unwind_next() assumes that the fp is valid. > > - unwind_frame() used to return an error value. unwind_next() only > sets an internal flag "failed" to indicate that an error was > encountered. This flag is checked by unwind_continue(). > > Reliability checks > ================== > > There are some kernel features and conditions that make a stack trace > unreliable. Callers may require the unwinder to detect these cases. > E.g., livepatch. > > Introduce a new function called unwind_check_reliability() that will detect > these cases and set a boolean "reliable" in the stackframe. > > unwind_check_reliability() will be called for every frame. That is, in > unwind_start() as well as unwind_next(). > > Introduce the first reliability check in unwind_check_reliability() - If > a return PC is not a valid kernel text address, consider the stack > trace unreliable. It could be some generated code. > > Other reliability checks will be added in the future. > > arch_stack_walk_reliable() > ========================== > > Introduce arch_stack_walk_reliable() for ARM64. This works like > arch_stack_walk() except that it returns an error if the stack trace is > found to be unreliable. > > Until all of the reliability checks are in place in > unwind_check_reliability(), arch_stack_walk_reliable() may not be used by > livepatch. But it may be used by debug and test code. > > SYM_CODE check > ============== > > This is the second reliability check implemented. > > SYM_CODE functions do not follow normal calling conventions. They cannot > be unwound reliably using the frame pointer. Collect the address ranges > of these functions in a special section called "sym_code_functions". > > In unwind_check_reliability(), check the return PC against these ranges. If > a match is found, then mark the stack trace unreliable. > > Last stack frame > ---------------- > > If a SYM_CODE function occurs in the very last frame in the stack trace, > then the stack trace is not considered unreliable. This is because there > is no more unwinding to do. Examples: > > - EL0 exception stack traces end in the top level EL0 exception > handlers. > > - All kernel thread stack traces end in ret_from_fork(). > --- > Changelog: > > v9: > From me: > > - Removed the word "RFC" from the subject line as I believe this > is mature enough to be a regular patch. > > From Mark Brown, Mark Rutland: > > - Split the patches into smaller, self-contained ones. > > - Always enable STACKTRACE so that arch_stack_walk() is always > defined. > > From Mark Rutland: > > - Update callchain_trace() take the return value of > perf_callchain_store() into acount. > > - Restore get_wchan() behavior to the original code. > > - Simplify an if statement in dump_backtrace(). > > From Mark Brown: > > - Do not abort the stack trace on the first unreliable frame. > > > v8: > - Synced to v5.14-rc5. > > From Mark Rutland: > > - Make the unwinder loop similar to other architectures. > > - Keep details to within the unwinder functions and return a simple > boolean to the caller. > > - Convert some of the current code that contains unwinder logic to > simply use arch_stack_walk(). I have converted all of them. > > - Do not copy sym_code_functions[]. Just place it in rodata for now. > > - Have the main loop check for termination conditions rather than > having unwind_frame() check for them. In other words, let > unwind_frame() assume that the fp is valid. > > - Replace the big comment for SYM_CODE functions with a shorter > comment. > > /* > * As SYM_CODE functions don't follow the usual calling > * conventions, we assume by default that any SYM_CODE function > * cannot be unwound reliably. > * > * Note that this includes: > * > * - Exception handlers and entry assembly > * - Trampoline assembly (e.g., ftrace, kprobes) > * - Hypervisor-related assembly > * - Hibernation-related assembly > * - CPU start-stop, suspend-resume assembly > * - Kernel relocation assembly > */ > > v7: > The Mailer screwed up the threading on this. So, I have resent this > same series as version 8 with proper threading to avoid confusion. > v6: > From Mark Rutland: > > - The per-frame reliability concept and flag are acceptable. But more > work is needed to make the per-frame checks more accurate and more > complete. E.g., some code reorg is being worked on that will help. > > I have now removed the frame->reliable flag and deleted the whole > concept of per-frame status. This is orthogonal to this patch series. > Instead, I have improved the unwinder to return proper return codes > so a caller can take appropriate action without needing per-frame > status. > > - Remove the mention of PLTs and update the comment. > > I have replaced the comment above the call to __kernel_text_address() > with the comment suggested by Mark Rutland. > > Other comments: > > - Other comments on the per-frame stuff are not relevant because > that approach is not there anymore. > > v5: > From Keiya Nobuta: > > - The term blacklist(ed) is not to be used anymore. I have changed it > to unreliable. So, the function unwinder_blacklisted() has been > changed to unwinder_is_unreliable(). > > From Mark Brown: > > - Add a comment for the "reliable" flag in struct stackframe. The > reliability attribute is not complete until all the checks are > in place. Added a comment above struct stackframe. > > - Include some of the comments in the cover letter in the actual > code so that we can compare it with the reliable stack trace > requirements document for completeness. I have added a comment: > > - above unwinder_is_unreliable() that lists the requirements > that are addressed by the function. > > - above the __kernel_text_address() call about all the cases > the call covers. > > v4: > From Mark Brown: > > - I was checking the return PC with __kernel_text_address() before > the Function Graph trace handling. Mark Brown felt that all the > reliability checks should be performed on the original return PC > once that is obtained. So, I have moved all the reliability checks > to after the Function Graph Trace handling code in the unwinder. > Basically, the unwinder should perform PC translations first (for > rhe return trampoline for Function Graph Tracing, Kretprobes, etc). > Then, the reliability checks should be applied to the resulting > PC. > > - Mark said to improve the naming of the new functions so they don't > collide with existing ones. I have used a prefix "unwinder_" for > all the new functions. > > From Josh Poimboeuf: > > - In the error scenarios in the unwinder, the reliable flag in the > stack frame should be set. Implemented this. > > - Some of the other comments are not relevant to the new code as > I have taken a different approach in the new code. That is why > I have not made those changes. E.g., Ard wanted me to add the > "const" keyword to the global section array. That array does not > exist in v4. Similarly, Mark Brown said to use ARRAY_SIZE() for > the same array in a for loop. > > Other changes: > > - Add a new definition for SYM_CODE_END() that adds the address > range of the function to a special section called > "sym_code_functions". > > - Include the new section under initdata in vmlinux.lds.S. > > - Define an early_initcall() to copy the contents of the > "sym_code_functions" section to an array by the same name. > > - Define a function unwinder_blacklisted() that compares a return > PC against sym_code_sections[]. If there is a match, mark the > stack trace unreliable. Call this from unwind_frame(). > > v3: > - Implemented a sym_code_ranges[] array to contains sections bounds > for text sections that contain SYM_CODE_*() functions. The unwinder > checks each return PC against the sections. If it falls in any of > the sections, the stack trace is marked unreliable. > > - Moved SYM_CODE functions from .text and .init.text into a new > text section called ".code.text". Added this section to > vmlinux.lds.S and sym_code_ranges[]. > > - Fixed the logic in the unwinder that handles Function Graph > Tracer return trampoline. > > - Removed all the previous code that handles: > - ftrace entry code for traced function > - special_functions[] array that lists individual functions > - kretprobe_trampoline() special case > > v2 > - Removed the terminating entry { 0, 0 } in special_functions[] > and replaced it with the idiom { /* sentinel */ }. > > - Change the ftrace trampoline entry ftrace_graph_call in > special_functions[] to ftrace_call + 4 and added explanatory > comments. > > - Unnested #ifdefs in special_functions[] for FTRACE. > > v1 > - Define a bool field in struct stackframe. This will indicate if > a stack trace is reliable. > > - Implement a special_functions[] array that will be populated > with special functions in which the stack trace is considered > unreliable. > > - Using kallsyms_lookup(), get the address ranges for the special > functions and record them. > > - Implement an is_reliable_function(pc). This function will check > if a given return PC falls in any of the special functions. If > it does, the stack trace is unreliable. > > - Implement check_reliability() function that will check if a > stack frame is reliable. Call is_reliable_function() from > check_reliability(). > > - Before a return PC is checked against special_funtions[], it > must be validates as a proper kernel text address. Call > __kernel_text_address() from check_reliability(). > > - Finally, call check_reliability() from unwind_frame() for > each stack frame. > > - Add EL1 exception handlers to special_functions[]. > > el1_sync(); > el1_irq(); > el1_error(); > el1_sync_invalid(); > el1_irq_invalid(); > el1_fiq_invalid(); > el1_error_invalid(); > > - The above functions are currently defined as LOCAL symbols. > Make them global so that they can be referenced from the > unwinder code. > > - Add FTRACE trampolines to special_functions[]: > > ftrace_graph_call() > ftrace_graph_caller() > return_to_handler() > > - Add the kretprobe trampoline to special functions[]: > > kretprobe_trampoline() > > Previous versions and discussion > ================================ > > v8: https://lore.kernel.org/linux-arm-kernel/20210812190603.25326-1-madvenka@linux.microsoft.com/ > v7: Mailer screwed up the threading. Sent the same as v8 with proper threading. > v6: https://lore.kernel.org/linux-arm-kernel/20210630223356.58714-1-madvenka@linux.microsoft.com/ > v5: https://lore.kernel.org/linux-arm-kernel/20210526214917.20099-1-madvenka@linux.microsoft.com/ > v4: https://lore.kernel.org/linux-arm-kernel/20210516040018.128105-1-madvenka@linux.microsoft.com/ > v3: https://lore.kernel.org/linux-arm-kernel/20210503173615.21576-1-madvenka@linux.microsoft.com/ > v2: https://lore.kernel.org/linux-arm-kernel/20210405204313.21346-1-madvenka@linux.microsoft.com/ > v1: https://lore.kernel.org/linux-arm-kernel/20210330190955.13707-1-madvenka@linux.microsoft.com/ > > Madhavan T. Venkataraman (11): > arm64: Select STACKTRACE in arch/arm64/Kconfig > arm64: Make perf_callchain_kernel() use arch_stack_walk() > arm64: Make get_wchan() use arch_stack_walk() > arm64: Make return_address() use arch_stack_walk() > arm64: Make dump_stacktrace() use arch_stack_walk() > arm64: Make profile_pc() use arch_stack_walk() > arm64: Call stack_backtrace() only from within walk_stackframe() > arm64: Rename unwinder functions, prevent them from being traced and > kprobed > arm64: Make the unwind loop in unwind() similar to other architectures > arm64: Introduce stack trace reliability checks in the unwinder > arm64: Create a list of SYM_CODE functions, check return PC against > list > > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/linkage.h | 12 ++ > arch/arm64/include/asm/sections.h | 1 + > arch/arm64/include/asm/stacktrace.h | 12 +- > arch/arm64/kernel/perf_callchain.c | 8 +- > arch/arm64/kernel/process.c | 38 ++-- > arch/arm64/kernel/return_address.c | 6 +- > arch/arm64/kernel/stacktrace.c | 274 +++++++++++++++++++--------- > arch/arm64/kernel/time.c | 22 ++- > arch/arm64/kernel/vmlinux.lds.S | 10 + > 10 files changed, 257 insertions(+), 127 deletions(-) > > > base-commit: 36a21d51725af2ce0700c6ebcb6b9594aac658a6 >